The present invention relates to a structure for mounting a solid-state imaging device such as a CCD (Charge Coupled Device) on a digital image capturing apparatus such as a digital camera.
Recently, a digital camera is used instead of a conventional camera which employs a silver-salt film for recording a captured optical image. In the digital camera, an optical image is captured by the imaging device and converted to digital image data so as to be recorded in an digital storage device such as a built-in memory or a detachable card-type memory.
When the imaging device is built in a camera, the imaging device is first soldered on a glass-epoxy circuit board, and the circuit board carrying the imaging device is then mounted on an optical unit. Please note that, in this specification, the “optical unit” is defined as an unit carrying a lens assembly, an infrared cutting filter and so on, and a photographing optical system of a digital camera is constituted by mounting a circuit board carrying the imaging device on the optical unit.
In the meantime, a solid-state imaging device having more than 2 million pixels has recently been put in practical use. In such a solid-state imaging device, the size of one pixel is so small that it becomes necessary for the imaging device to be mounted on the optical unit with very high positioning accuracy. That is, in order to obtain precise image data, the light receiving surface of the imaging device must align with the focusing surface of the photographing optical system with high accuracy. If the light receiving surface of the imaging device is tilted with respect to and/or displaced from the focusing surface of the photographing optical system, it becomes difficult to obtain precise data at the respective pixels.
With the above-explained conventional mounting structure, however, the positioning accuracy required for the imaging device of high pixel resolution can hardly be obtained, due to the uneven thickness of the solder layer with which the imaging device is adhered to the circuit board and/or to the inherent warp of the glass-epoxy circuit board itself.
There have been various other structures for mounting a solid-state imaging device on an optical unit, with which, however, the imaging device can hardly be mounted on the optical unit with the required positioning accuracy and/or with efficient workability.